The physical quantity measuring sensor is exemplified by a pressure sensor including a sensor module that is provided in a joint, the sensor module including a detection portion that detects the pressure of the target fluid.
Some of the sensor module of the pressure sensor are ceramic. A typical ceramic sensor module includes: a plate-shaped diaphragm body; an annular supporting portion connected to the diaphragm body; a recess at the center of a first surface of the diaphragm body; a step formed between an inner surface of the recess and the first surface; and a connecting portion between the first surface of the diaphragm body and an inner surface of the annular supporting portion, in which a cross section from the connecting portion and the step is curved (Patent Literature 1: Japanese Patent No. 4828804).
In order to prevent leakage of the target fluid, it is desirable that the sensor module is integrally bonded to the projection of the joint. If both the sensor module and the joint are metallic, the sensor module and the joint can be integrally bonded to each other by welding. However, when the sensor module is ceramic, the sensor module cannot be welded to the metallic joint.
When the sensor module cannot be bonded to the joint, the target fluid leaks from between the sensor module and the joint. Accordingly, an O-ring is used for attaching the sensor module to the joint.
In a typical structure in which the sensor module is attached to the joint using the O-ring, the O-ring is disposed between an inner wall of a cavity of a ceramic pressure-sensitive element and a cylindrical projection of a housing, and a washer is crimped to be fixed to a tip end of the cylindrical projection, thereby preventing the O-ring from slipping off (Patent Literature 2: JP-A-2006-78379).
In Patent Literature 2, a groove in which the O-ring is held is defined by a step, which is formed at a base end of the cylindrical projection and with which the O-ring is engaged, and the washer crimped at the tip end of the cylindrical projection.
Moreover, this pressure sensor includes a connector provided with a terminal and a housing provided with the sensor module, in which a signal detected at the sensor module is transmitted to the terminal through an electronic component.
This pressure sensor is exemplified by a typical pressure sensor including: a diaphragm member having a detection portion; a flexible circuit board having a first end connected to the detection portion; an amplifier circuit provided by circuit components and mounted at a second end of the flexible circuit board; and a connector attached with the second end of the flexible circuit board at which the circuit components are mounted (Patent Literature 3: JP-A-2002-310826).
A typical pressure sensor in a different type includes: a sensitive-pressure element; an output terminal; a flexible circuit board connecting the sensitive-pressure element to the output terminal; an ASIC mounted on the flexible circuit board; and a connector connected to an end of the output terminal (Patent Literature 2).
In the typical example of Patent Literature 1, although stress generating at the connecting portion between the diaphragm body and the annular support is reduced, a structure for attaching the ceramic sensor module to the metallic joint is not disclosed.
In the typical example of Patent Literature 1, in order to attach the sensor module to the joint using the O-ring, it is conceivable to form a projection on the joint and attach the sensor module to the projection via the O-ring. However, in such a structure, a cross-sectionally square C-shaped groove for holding the O-ring needs to be separately machined to the projection, so that the manufacturing cost of the pressure sensor is increased.
In other words, the groove for holding the O-ring needs to have a depth and a width corresponding to the dimension of the O-ring. When the width of the groove is narrower than the O-ring, the O-ring cannot be fitted into the groove. On the other hand, when the width of the groove is wider, the width of the projection from the groove to a tip end is decreased, whereby the tip end of the projection is likely to be broken or the like. Such breakage or the like of the tip end of the projection is prevented by keeping a position of the groove apart from the tip end of the projection. However, the projection itself is lengthened, and consequently, the physical quantity measuring sensor itself is also lengthened.
In the typical example of Patent Literature 2, the structure of crimping to fix the washer at the tip end of the cylindrical projection is applied for holding the O-ring to the cylindrical projection of the housing. In the typical example of Patent Literature 2, the structure of the cross-sectionally square C-shaped groove for holding the O-ring becomes complicated, thereby increasing the manufacturing cost of the pressure sensor.
Moreover, in the typical examples of Patent Literatures 2 and 3, the structure of attaching the electronic component to the flexible circuit board is applied for electrically connecting the circuit component and the electronic component of the ASIC to the sensor module. For this reason, in these typical examples, attachment of the electronic component to the flexible circuit board and assembly of the pressure sensor become complicated, thereby increasing the manufacturing cost of the pressure sensor.
In other words, since the flexible circuit board is easily bent, the flexible circuit board needs to be fixed to a holder or the like so as to attach the electronic component to a planar surface of the board, so that an operation is complicated. Further, in assembly of the pressure sensor, a first end of the flexible circuit board needs to be connected to the sensor module while a second end of flexible circuit board needs to be connected to the terminal. During this connection operation, the electronic component bonded to the flexible circuit board needs to be kept from slipping off from the flexible circuit board.